Power operated torque tool

ABSTRACT

In a power operated torque tool, the pressure-fluid feed is controlled by a valve which opens to start the tool, and closes to stop it. This valve is mounted on the end of a push-rod which extends along the axis of the tool. The tool also has a clutch which disengages on reaching a predetermined torque, and at the same time releases a grip on the push-rod, so that the valve can move to close the feed to the tool motor, and thus to stop the tool. The grip on the push-rod is exerted by a group of balls held in a sleeve and pushed against the rod by a tube with a tapered internal wall which surrounds the sleeve. The balls are pushed against the taper by a light spring, which is considerably weaker than the spring which holds the clutch in engagement.

The invention relates to a power operated torque tool having an axis andcomprising a pressure fluid driven motor, a valve controlling thepressure fluid flow to the motor, a torque responsive clutch having aclutch member adapted to move axially when the torque delivered exceedsa predetermined level, a tubular member carrying the drive from themotor to the clutch, and a push rod extending along the axis of the toolbetween the clutch and the valve for operating the valve on movement ofthe clutch member.

There are two known methods of cutting out the drive to the tool bit. Inthe first, a clutch is provided, and at the predetermined torque theclutch moves axially to disconnect the drive. A tool using this methodis shown in our British patent specification No. 1,289,056. With thismethod the motor continues to run after the drive to the tool bit hasdisconnected, and therefore wastes compressed air.

In the second method, with which this specification is particularlyconcerned, a valve in the pressure fluid feed to the motor is closedautomatically at the predetermined torque and the tool therefore stops.A tool of this type is described in British patent specification No.1,263,238. In this specification, a valve operating member is gripped bya number of balls arranged around the operating member and cammed intoengagement with the member by a ramped surface. This ramped surface isbiased into the operating, rod-gripping position by means of acompression spring which also governs the predetermined level at whichthe clutch of the tool will disengage. However, since this one springhas to perform two functions the force which it exerts is unlikely to bethe ideal force for either object. The spring must be more powerful forthe purpose of determining the torque than is necessary for maintainingthe gripping balls in engagement with the operating member. This invitesunnecessary wear.

It is an object of this invention to avoid unnecessary wear by ensuringthat the force applied to the clutch for the purpose of determining themaximum torque and the force applied to the operating member grippingarrangement are both suited to their particular functions.

The invention is characterised by the provision of a sleeve inside thetubular member, which sleeve moves axially with one clutch member whenthe predetermined torque is developed, a ramped surface on the inside ofthe tubular member, a plurality of bores in the wall of the sleeve, andgripping members in each of the bores, which can be urged through thebores by the ramped surface in order to grip the push rod inside thesleeve, and on movement of the ramped surface away from the grippingmembers, to release the push rod.

In addition to the arrangement for closing the air valve at thepredetermined torque, the tool may incorporate a clutch device asdescribed in our previously mentioned British Pat. No. 1,289,056. Thedisengagement mechanism of the tool then has the advantages of bothdifferent disengagement mechanisms.

The invention will now be further described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a section through a screwdriver according to the invention,

FIG. 2 is a part-section corresponding to FIG. 1, but showing thescrewdriver applied to a screw with pressure applied,

FIG. 3 is also a part-section corresponding to FIG. 1, but showing thescrew screwed up tight, and the screwdriver stopped, the required torquehaving been reached, and

FIG. 4 is a section of FIG. 1 on an enlarged scale, taken between thelines A--A and B--B in FIG. 1.

The screwdriver shown in the figures is driven by a sliding vanepneumatic motor through a gear system, neither of which parts are shown.

The pneumatic motor is fed with compressed air from a duct 1. The airflow is controlled by a valve 2 which sits on a valve seat 3. The valveis opened by a push-rod 4 which lifts the valve 2 off its seat 3 againstthe pressure of the air in duct 1. Air then passes to the motor alongduct 5. A light spring 6 is provided in the duct 1 to keep the valve 2in place while the tool is not in use. When the push-rod is released thepressure of the air plus the pressure of the spring closes the valve.

The push-rod 4 passes through the centre of the motor and gear systemwithout interacting with them in any way.

The output drive from the gear system is passed to a hollow shaftmounted in bearings 8. A tubular member 9 is splined to the shaft 7 at10, so that the member rotates with the shaft 7, while being able tomove axially relative to it.

At the left-hand end of the tubular member 9 is a torque responsivemeans, to be seen best in FIG. 4, which comprises two parts 11 and 12 ofa first clutch which move apart axially at a predetermined torque. Inthis embodiment, the part 11 is axially immovable, and the part 12 movesaway from it. The two parts 11 and 12 have complementary annular rampedsurfaces, a ball 13 being inserted in a gap left between the two partsto facilitate the riding up of part 12 on the ramped surfaces. The part12 is keyed to the tubular member 9 by balls 14 which enter a slot 15.The part 11 rotates with the part 12 due to the engagement of theirramped surfaces, but can also rotate relative to part 12 on the ballbearings 16 when the predetermined torque has been reached.

When the part 12 moves apart from part 11 at the predetermined torque,(to the right in the figure) it moves against the pressure ofcompression spring 17 and moves with it an annular sleeve 18 forming apart of a second clutch. The sleeve 18 has gear teeth 19 or splines onits inner cylindrical surface, and these teeth mate with correspondingteeth 20 on the outer periphery of the part 11, and with correspondingteeth 21 on the outer periphery of the screwdriver bit holder 22. Thus,when the parts 11 and 12 are close together, the sleeve 18 surrounds theteeth 20 and 21 of both the part 11 and the holder 22 (see FIG. 1) anddrive is transmitted to the screwdriver bit 23. When the parts 11 and 12have moved apart (see FIG. 3), the sleeve 18 of the second clutch iswithdrawn from the teeth 21, and thus drive is no longer transmitted tothe holder 22. A thrust bearing 24 permits the tubular member 9 tocontinue rotating without entraining the holder 22. At this stage, thetorque drops to zero and the first clutch parts 11 and 12 move togetheragain. However, the sleeve 18 will not re-engage with the teeth 21,because it is being biased towards these teeth only by the light spring40, and it is rotating at a considerable speed. This non-engagementmechanism is described in full in our British Pat. No. 1,289,056.

It will therefore be seen that when the part 12 moves away from part 11at the predetermined torque, the drive is disengaged from thescrewdriver bit 23. However, this still leaves the motor running andwasting compressed air. This invention provides means for shutting offthe motor when the predetermined torque is reached, as will now bedescribed.

The screwdriver shown in FIG. 1 is not operating, while the screwdriverof FIG. 2 is. To get from the position of FIG. 1 to FIG. 2, thescrewdriver bit 23 must be pushed against the screw 25 being screwed up,to move the operative parts shown in the figures to the right relativeto the tool housing 26, and relative to the shaft 7 where the spliningat 10 maintains a driving connection. This movement causes the push rod4 to be moved to open the valve 2, and thus to admit compressed air tooperate the motor.

The left-hand end of the rod 4 is gripped in the operating position bythree balls arranged in circumferentially spaced bores 28 in a sleeve29. The balls 27 are pushed against the rod 4 by a tapered part 30 ofthe tubular member 9. The sleeve 29 is pushed towards the tapered partby compression spring 31, so that the balls grip the rod.

When the part 12 moves away from the part 11 at the predeterminedtorque, the part 12 moves a cross pin 32 as well as the sleeve 18. Thepin moves axially in a gap 33 in the tubular member 9. The sleeve 29abuts the pin 32 and is therefore moved to the right, against thepressure of spring 31 so that the balls 27 move away from the taperedpart, and are no longer forced against the push-rod 4. The push-rod istherefore no longer gripped at its left-hand end, and the air pressurein the duct 1 plus the pressure of the spring 6 will then close thevalve member 2 onto its seat 3, and push the push-rod into the positionshown in FIG. 3, to stop the motor.

When the tool is removed from the screw, the spring 31 will return thesleeve 29, surrounding the push-rod 4, back to its starting position. Onits way back, the balls 27 in the sleeve 29 will not push the push-rod 4out of position, because of the collar 34 on the rod which limits itsmovement to the left. The tool will then be reset ready for performing anew operation.

The screwdriver bit 23 has a hexagonal portion 35 which fits into ahexagonal socket in the holder 22. The bit is held in place byspring-loaded balls 36 which engage a recess 37 in the bit. Thescrewdriver bit can be exchanged for a bit of any other form.

The push-rod is made in several sections, the sections abutting eachother so that a pushing motion can be transmitted, but the rotary motionof one section is transmitted to the next section at a lower rate sothat the valve member 2 is not itself required to rotate.

The predetermined torque can be adjusted by moving the rear abutment 38of the spring 17 which is carried on a thread 39. Alternatively or inaddition, the spring 17 can be replaced by one of differentcharacteristics.

I claim:
 1. A pressure-fluid operated torque tool havinga pressure-fluid driven motor, a valve controlling the flow of pressure fluid to the motor, a torque-responsive clutch having a clutch member adapted to move axially when the torque delivered exceeds a predetermined level, a tubular member carrying the drive from the motor to the clutch, and having an internally-tapered portion, a push-rod extending centrally through the tubular member, a plurality of rod-engaging balls arranged between the tapered portion of the tubular member and the rod, to be forced against the rod by the tapered portion to grip the rod, and a cage for supporting the balls, which cage is moved axially by said axially movable clutch member, when the predetermined torque level is reached, to release the grip of the balls on the rod; and below the predetermined torque is biassed by a spring to bring the balls into cooperation with the tapered portion, where they grip the rod.
 2. A tool as claimed in claim 1, wherein the cage for supporting the balls is in the form of a sleeve which has three bores therein, each bore supporting one ball.
 3. A tool as claimed in claim 2, wherein the torque-responsive axially movable clutch member comprises two halves one of which moves apart from the other along the axis to move the sleeve when the predetermined torque level is reached.
 4. A tool as claimed in claim 3, wherein the torque-responsive clutch member controls a second clutch which disengages the drive when the two halves of the torque-responsive clutch member move apart.
 5. A tool as claimed in claim 1, wherein the motor is a pneumatic motor.
 6. A tool as claimed in claim 1, wherein the push-rod is divided along its length into sections which abut one another to transmit a pushing force, but are not otherwise connected. 